Capacitor with stoichiometrically adjusted dielectric and method of fabricating same

ABSTRACT

A capacitor and a capacitor dielectric material are fabricated by adjusting the amount of an ionic conductive species, such as hydrogen, contained in the capacitor dielectric material to obtain predetermined electrical or functional characteristics. Forming the capacitor dielectric material from silicon, nitrogen and hydrogen allows a stoichiometric ratio control of silicon to nitrogen to limit the amount of hydrogen. Forming the capacitor by dielectric material plasma enhanced chemical vapor deposition (PECVD) allows hydrogen bonds to be broken by ionic bombardment, so that stoichiometric control is achieved by controlling the power of the PECVD. Applying a predetermined number of thermal cycles of temperature elevation and temperature reduction also breaks the hydrogen bonds to control the amount of the hydrogen in the formed capacitor dielectric material.

CROSS-REFERENCE TO RELATED INVENTIONS

[0001] This invention is related to the following inventions, all ofwhich are assigned to the assignee of the present invention: High AspectRatio Metal-to-Metal Linear Capacitor for an Integrated Circuit, U.S.patent application Ser. No. 09/052,851, filed Mar. 31, 1998; Method ofElectrically Connecting and Isolating Components with Vertical ElementsExtending between Interconnect Layers in an Integrated Circuit, U.S.patent application Ser. No. 09/052,793, filed Mar. 31, 1998; VerticalInterdigitated Metal-Insulator-Metal Capacitor for an IntegratedCircuit, U.S. patent application Ser. No. 09/219,655, filed Dec. 23,1998; Method of Forming and Electrically Connecting a VerticalInterdigitated Metal-Insulator-Metal Capacitor Extending betweenInterconnect Layers in an Integrated Circuit, U.S. patent applicationSer. No. 09/221,023, filed Dec. 23, 1998; Interconnect-IntegratedMetal-Insulator-Metal Capacitor and Method of Fabricating Same, U.S.patent application Ser. No. 09/559,934, filed Apr. 27, 2000;Interconnect-Embedded Integrated Metal-Insulator-Metal Capacitor andMethod of Fabricating Same, U.S. patent application Ser. No. 09/496,971,filed Feb. 2, 2000; Capacitor with Multiple-Component Dielectric andMethod of Fabricating Same; U.S. patent application Ser. No. ______ (LSIDocket No. 99-130), filed concurrently herewith; and Encapsulated-MetalVertical-Interdigitated Capacitor and Damascene Method of ManufacturingSame; U.S. patent application Ser. No. 09/525,489, filed Mar. 15, 2000.The disclosures of these aforementioned U.S. patent applications arehereby incorporated herein by this reference.

FIELD OF THE INVENTION

[0002] This invention relates to electrical capacitors. Moreparticularly, the present invention relates to a new and improvedcapacitor having a dielectric material which has been stoichiometricallyformed or treated to optimize or improve the electrical or functionalcharacteristics of the capacitor, such as its capacitance valuevariation or tolerance, its change-in-capacitance per change-in-voltage(dC/dV), or its leakage current. Optimizing these characteristicsachieves more reliable and predictable functionality, as well as preciseoperating characteristics, thereby making the capacitor more suitablefor both analog and digital circuit functions when incorporated withinan integrated circuit (IC).

BACKGROUND OF THE INVENTION

[0003] Capacitors are commonly employed in ICs for a variety ofpurposes, such as to condition signals, to store electrical charge, toblock DC voltage levels, and to stabilize power supplies. In memory ICs,a capacitor is used to hold enough charge to represent a detectablelogic state.

[0004] Polysilicon is typically used to construct the electrode platesof the capacitor in a substrate of the IC. The diffusion and dopingcharacteristics of polysilicon result in variable capacitancecharacteristics, in which the capacitance value varies relative to thevoltage level applied to the capacitor and the temperature experiencedby the capacitor. Despite the variable characteristics of polysiliconcapacitors, the capacitance variation is not of primary concern indigital memory ICs. Memory capacitors are required only to acceptcharge, to hold some or all of the charge for a finite time period andthen discharge, all in a reliable manner. Furthermore, since polysiliconis also used to fabricate other components of the IC, such astransistors and conductors, the plates of the capacitors can be formedsimultaneously with the other components of the IC.

[0005] In analog and mixed signal circuit applications, on the otherhand, capacitors are frequently used as impedance elements whoseresponse characteristic must be linear. If the impedance of thecapacitor is not fixed and reliably ascertainable, the capacitanceresponse of the capacitor relative to voltage will vary non-linearly,causing unacceptable variations in the performance of the analog ormixed signal circuit.

[0006] Application specific integrated circuits (ASICs) sometimescombine analog circuitry with digital circuitry on the same substrate.In such applications, the fabrication of capacitors has become somewhatproblematic. Polysilicon is a semiconductor, which is not the bestmaterial to use as an electrode to form a capacitor. A space chargelayer forms in the doped polysilicon and adversely affects thecapacitance vs. voltage response (linearity) and the frequency responseof the capacitor. When a metal material is used for the electrode,however, no space charge layer exists.

[0007] Many contemporary ICs employ multiple layers of interconnects, asan adjunct of their miniaturization. Interconnects are layers ofseparate electrical conductors which are formed overlying the substrateand which electrically connect various functional components of the IC.Because of space and volume considerations in ICs, attention has beenfocused upon the effective use of the space between the interconnectlayers. Normally the space between the interconnect layers is occupiedby an insulating material, known as an intermetal dielectric (IMD). Oneeffective use for the space between the interconnect layers is to formcapacitors in this space using the interconnect layers. The previouslyreferenced U.S. patent applications focus on different techniques forcombining capacitors with the conductors of the interconnect layers toachieve desirable effects within the IC.

[0008] Because the conductors of the interconnect layers are of metalconstruction, the capacitors formed between the interconnect layers arepreferably of a metal-insulator-metal (MIM) construction. A MIMcapacitor has metal plates, usually formed on the metal conductors ofthe interconnect layers. The fourth and fifth above identified patentapplications describe techniques for forming the metal capacitor plateswith the conductors of the interconnect layers. The additional benefitof MIM capacitors is that they possess a higher degree of linearity andan improved frequency response. Unlike polysilicon capacitors, MIMcapacitors incorporated within the interconnect levels are unobtrusiveto the underlying digital components or circuitry.

[0009] The use of a MIM capacitor within the interconnect levels canalso reduce the size of the overall IC structure because the digitalcircuitry exists under the capacitor, instead of beside it.Additionally, MIM capacitors are readily fabricated as part of theinterconnect layers without a significant increase in the number ofprocess steps or in the manufacturing costs. Connecting the MIMcapacitors in the interconnect layers to the appropriate components ofthe IC is relatively easily accomplished by post-like or plug-like “viainterconnects” that extend between the interconnect layers as needed.

[0010] However, even the more linear MIM capacitors are susceptible tonon-linear performance under the influence of different electrical andphysical conditions, and even relatively small deviations from theexpected and desired performance may be sufficient to diminish theeffective use of such capacitors in precise linear or analog circuits orin digital circuits.

[0011] It is with respect to these and other background considerationsthat the present invention has evolved.

SUMMARY OF THE INVENTION

[0012] The improvements of the invention relate to the discovery thatthe density of the film which represents the bonding network along withthe incorporation of bonded and free hydrogen in capacitor dielectricmaterials, such as silicon nitride, silicon oxynitride or silicondioxide, can induce undesirable electrical and functional effects. Suchundesirable effects include excessive variability or tolerance in theelectrical characteristics of the capacitor, excessivechange-in-capacitance per change-in-voltage (dC/dV, referred to as thelinear response) characteristics, and excessive leakage current.

[0013] The present invention makes use of this discovery by controllingthe stoichiometry of the dielectric, the dielectric depositionconditions, the network bonding (i.e. density) and the hydrogenincorporation. In the case where the dielectric film is comprised ofeither an oxide or oxynitride film the density and hydrogen content canbe manipulated by post deposition thermal anneals.

[0014] By eliminating excess hydrogen within the capacitor dielectricmaterial and controlling the stoichiometry of the dielectric film,improvements or optimizations are obtained in the electrical andfunctional characteristics of the capacitor dielectric material. Suchcharacteristics include the capacitor's capacitance density, its linearresponse (dC/dV), and its leakage current.

[0015] The improvements of the present invention also relate to therecognition that the density and the amount of bonded and free hydrogenin a silicon nitride or silicon oxynitride capacitor dielectric materialmay be indirectly controlled and optimized. Such control andoptimization achieve the desirable electrical and functional effects bycontrolling the ratio of silicon and nitrogen used in forming thesilicon nitride or silicon oxynitride capacitor dielectric material.

[0016] These and other improvements are achieved in methods offabricating a capacitor dielectric material in a capacitor. Onefabrication aspect of the invention includes forming the capacitordielectric material to contain hydrogen, and adjusting the compositionof the capacitor dielectric material by controlling the stoichiometry ofthe capacitor dielectric material in order to adjust the amount of thehydrogen contained in the capacitor dielectric material and to obtainpredetermined electrical or functional characteristics of the capacitor.Preferably, the capacitor dielectric material is formed from substancesincluding silicon, nitrogen and hydrogen. Also, a stoichiometric ratioof silicon to nitrogen is preferably controlled to limit the amount ofhydrogen in the capacitor dielectric material. The ratio of silicon tonitrogen is preferably approximately 1.0 or less, or even morepreferably approximately 0.75.

[0017] Another fabrication aspect of the invention relates to formingthe capacitor dielectric material to include hydrogen bonds bydepositing the substances by using plasma enhanced chemical vapordeposition, breaking some of the hydrogen bonds by ionic bombardment toallow the hydrogen from the broken bonds to escape from the capacitordielectric material, and controlling the amount of the hydrogen in theformed capacitor dielectric material by controlling the power and amountof ionic bombardment.

[0018] Still another fabrication aspect of the invention involvesbreaking hydrogen bonds to the capacitor dielectric material by applyingat least one thermal cycle of temperature elevation and temperaturereduction of the capacitor dielectric material, and controlling theamount of the hydrogen in the formed capacitor dielectric material bycontrolling the number and extent of the applications of thermal cyclesto the capacitor dielectric material.

[0019] Broader aspects of the present invention apply to capacitordielectric materials containing substances which, like hydrogen, have atendency to promote ionic conduction in the capacitor dielectricmaterial. Aspects of the present invention also relate to capacitorshaving dielectric materials formed by the method aspects of the presentinvention.

[0020] A more complete appreciation of the present invention and itsscope, and the manner in which it achieves the above noted improvements,can be obtained by reference to the following detailed description ofpresently preferred embodiments of the invention taken in connectionwith the accompanying drawings, which are briefly summarized below, andthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a partial, vertical cross-sectional view of a capacitorhaving dielectric material which has been stoichiometrically adjusted inaccordance with the present invention.

[0022]FIG. 2 is a normalized graph of exemplary change-in-capacitanceper change-in-voltage (dC/dV) characteristics of silicon nitride used asthe dielectric material of a capacitor.

[0023]FIG. 3 is a normalized graph of exemplary change-in-capacitanceper change-in-voltage (dC/dV) characteristics of silicon dioxide used asthe dielectric material of a capacitor.

[0024]FIG. 4 is a graph illustrating an exemplary change in the range ofthe capacitance values across the operating voltage relative to hydrogencontent of silicon nitride capacitor dielectric material.

[0025]FIG. 5 is a graph illustrating an exemplary range of dC/dVcharacteristics of a capacitor relative to hydrogen content of a siliconnitride capacitor dielectric material.

[0026]FIG. 6 is a graph illustrating the relationship between totalhydrogen content and a ratio of silicon to nitrogen in a silicon nitridecapacitor dielectric material.

[0027]FIG. 7 is a graph illustrating an exemplary amount of capacitorleakage current relative to a ratio of silicon-hydrogen bonds tosilicon-nitrogen-bonds of silicon nitride capacitor dielectric material.

[0028]FIG. 8 is a simplified block flow diagram illustrating theformation of stoichiometrically adjusted silicon nitride from silane,ammonia and nitrogen, in accordance with the present invention.

[0029]FIG. 9 is a simplified block flow diagram illustrating theformation of stoichiometrically adjusted silicon oxynitride from silane,ammonia, nitrogen and oxygen, in accordance with the present invention.

[0030]FIG. 10 is a simplified block flow diagram illustrating theformation of stoichiometrically adjusted silicon nitride andstoichiometrically adjusted silicon oxynitride (shown in dashed lines)by controlling and adjusting the power applied during plasma enhancedchemical vapor deposition of the capacitor dielectric material, inaccordance with the present invention.

[0031]FIG. 11 is a simplified block diagram illustrating the formationof stoichiometrically adjusted silicon dioxide by applying repetitivethermal cycles to the silicon dioxide after it has been formed as thecapacitor dielectric material, in accordance with the present invention.

DETAILED DESCRIPTION

[0032] A capacitor 20 which embodies the present invention is shown inFIG. 1. The capacitor 20 may be incorporated in an integrated circuit(IC) (not shown), either in or on a substrate of the IC or as part ofthe interconnect layers. The capacitor 20 has a pair of electrode plates22 and 24, hereinafter referred to as the upper and lower plates,respectively. The plates 22 and 24 are separated by adjacent capacitordielectric material 26. The capacitor dielectric material 26 has beenstoichiometrically adjusted to reduce the bonded hydrogen content, inaccordance with the present invention, as is discussed in greater detailbelow.

[0033] The upper and lower plates 22 and 24 are preferably formed of ametal material; or in appropriate circumstances, a semiconductormaterial. In the case were the upper and lower plates 22 and 24 areformed substantially by metal material, such as copper or aluminumconductors of an interconnect layer, the electrical and functionalcharacteristics of the capacitor 20 will be dictated primarily by thechoice and content of the capacitor dielectric material 26. In the casewhere the upper and lower plates 22 and 24 are formed of semiconductoror other principally non-metallic material, the material of the plates22 and 24 should be selected to coordinate with the capacitor dielectricmaterial 26 in enhancing the electrical and functional characteristicsof the capacitor.

[0034] The composition of the capacitor dielectric material 26 can beadjusted to optimize or improve certain functional and electricalcharacteristics of the capacitor 20. For example, one characteristicwhich may be improved by adjustment of the capacitor dielectric material26 is the change-in-capacitance per change-in-voltage (dC/dV)characteristic of the capacitor. FIG. 2 illustrates the typical dC/dVcharacteristic of a capacitor having metal plates with a singledielectric material formed of silicon nitride. As shown in FIG. 2, acurved line 32 shows that the capacitance value varies according to thevoltage applied across the capacitor plates. The fact that the line 32is curved demonstrates that the response characteristics of thecapacitor are nonlinear. Vertical bars 34 at points along the curve 32indicate the statistics of the measurements made for capacitance at eachvoltage selection. FIG. 2 shows the change in the mean of normalizedcapacitance over the voltage range of interest. The vertical bars 34show the range in normalized capacitance measured at each voltagesetting. Smaller vertical bars 34 indicate that the responsecharacteristics of the capacitor dielectric material 26 (FIG. 1) arefairly consistent along the curve 32, even though the curve 32 itself isnonlinear.

[0035]FIG. 3 illustrates the typical dC/dV characteristics of acapacitor having metal plates with a single dielectric material formedof silicon dioxide. In the situation illustrated in FIG. 3, curve 36generally represents the change in capacitance relative to the change involtage across the capacitor plates. Unlike curve 32 shown in FIG. 2,curve 36 shown in FIG. 3 is considerably more linear. Therefore, theresponse characteristics of a capacitor formed with silicon dioxidecapacitor dielectric material should be more linear than the responsecharacteristics of a capacitor formed with silicon nitride capacitordielectric material (FIG. 2). Vertical bars 38 at points on the curve 36show the range in measured normalized capacitance values at each voltagesetting. Some of vertical bars 38 show a considerable variation invalue, indicating that the curve 36 is subject to a considerable degreeof variability, particularly when the capacitor is subject to positivevoltages.

[0036] It has been discovered that the characteristics shown in FIGS. 2and 3, and others, are directly influenced and attributable to theextent of hydrogen within and the stoichiometry of silicon nitride andsilicon oxynitride capacitor dielectric materials. FIG. 4 shows thechange or range in the mean values of normalized capacitance (“capacitorrange”) over the entire voltage range of the measurement as shown inFIGS. 2 and 3. This change, or range, indicates the degree of linearityof a capacitor relative to hydrogen concentration.

[0037] Curve 40 of FIG. 4 shows that the capacitor range increases indirect relationship to the total amount of bonded hydrogen in thecapacitor dielectric material. Curve 40 represents the total bondedhydrogen within silicon nitride capacitor dielectric material. As thetotal amount of bonded hydrogen decreases, the capacitor range alsodecreases, indicating that the linearity of the capacitor improves withdiminished hydrogen content. A reduced tolerance or degree ofvariability is desired, because capacitors of the predicted size can bemore reliably fabricated, and their function within the electroniccircuit is more predictable.

[0038] Curve 42 shown in FIG. 4, illustrates nitrogen-hydrogen bonds inthe capacitor dielectric material. As a number of nitrogen-hydrogenbonds decreases, so does the capacitor range. On the other hand, curve44 shown in FIG. 4, which illustrates the number of silicon-hydrogenbonds in the capacitor dielectric material, shows that the number ofsilicon-hydrogen bonds have little effect on the capacitor range,because the slope of curve 44 is almost flat. Thus, curves 40 and 42show that reducing the total hydrogen bond content and thenitrogen-hydrogen content of the capacitor dielectric material willreduce the capacitor range.

[0039] A situation similar to that shown in FIG. 4 is illustrated inFIG. 5. FIG. 5 shows the range or change in slope (dC/dV) of the line ateach voltage setting. The expected range of dC/dV characteristicsrelative to the hydrogen content of silicon nitride capacitor dielectricmaterial is shown in FIG. 5. Curve 50 illustrates total hydrogencontent, which when reduced, results in a reduction in the range ofdC/dV characteristics. Curve 52 shows the contribution ofnitrogen-hydrogen bonds to the dC/dV characteristics. Reducing thenumber of nitrogen-hydrogen bonds also reduces the range of dC/dVvalues. On the other hand, curve 54, which represents the contributionof silicon-hydrogen bonds, again illustrates that a relatively minimaleffect on the dC/dV range results because of silicon-hydrogen bonds. Itis desirable to reduce the range of dC/dV characteristics of capacitors,because doing so results in capacitor functionality which is moreclosely related to the expected and predicted performance in theelectrical circuit in which the capacitor is used.

[0040] It is believed that the less desirable electrical and functionalcharacteristics of a capacitor which result from a relatively highhydrogen content of its capacitor dielectric material (at least in thecase of silicon nitride and silicon oxynitride), occur because of theaddition of hydrogen to the structural network of the dielectricmaterial. Free or weekly bonded hydrogen is an ion that can diffusethrough the dielectric material under an electric field. The hydrogenbecomes an ionic current carrying species which can reduce thedielectric constant of the material and the capacitance value of thecapacitor. Furthermore, an increase in ionic conduction can introducethe variability in the normalized capacitance range and dC/dVcharacteristics as illustrated in FIGS. 4 and 5 and by the magnitude ofthe vertical bars 34 and 38 shown in FIGS. 2 and 3, respectively. Insummary, greater ionic conduction is related to a higher hydrogencontent in a capacitor dielectric material, and the greater ionicconduction results in the less desirable electrical and functionalcharacteristics evidenced by larger values in capacitor range and dC/dVvalues shown for silicon nitride and oxynitride films. The same andsimilar electrical and functional characteristics are also believed tooccur in other types of capacitor dielectric material, and thesecharacteristics are also believed to be influenced by the hydrogencontent in the capacitor dielectric material.

[0041] A technique for controlling the amount of hydrogen content insilicon nitride and silicon oxynitride capacitor dielectric material isto control the silicon to nitrogen ratio when forming the capacitordielectric material. Curve 60 shown in FIG. 6 illustrates that the totalhydrogen content is directly related to the silicon to nitrogen ratio.If the silicon to nitrogen ratio is reduced, the total hydrogen contentis likewise reduced. Reducing the silicon to nitrogen ratio improves theelectrical and functional characteristics, by reducing the hydrogencontent.

[0042] Further confirmation of the importance of reducing the hydrogencontent of the capacitor dielectric material is shown in FIG. 7, where aratio of silicon-hydrogen bonds to nitrogen-hydrogen bonds is related tocapacitor leakage current as shown by curve 70. Reducing the ratio ofsilicon-hydrogen bonds to nitrogen-hydrogen bonds significantlydecreases the leakage current of the capacitor dielectric material. Ofcourse, a decreased capacitor leakage current characteristic isdesirable for capacitor dielectric material because the capacitordielectric material is more effective in preventing ionic conduction andin achieving electrical field charge storage.

[0043] Curve 60, shown in FIG. 6, illustrates that a technique ofcontrolling the hydrogen content of the capacitor dielectric film may beachieved by controlling the ratio of silicon to nitrogen in thecapacitor dielectric material. The ratio of the silicon-hydrogen bondsto the nitrogen-hydrogen bonds is directly related to the ratio ofsilicon to nitrogen. By lowering the ratio of silicon to nitrogen, thetotal hydrogen content is diminished. A ratio of silicon to nitrogen ofapproximately 1.0 or less obtains very desirable electrical andfunctional characteristics in capacitor dielectric material. Anextension of curve 60 indicates that a silicon to nitrogen ratio ofapproximately 0.75 is the absolute or best attainable stoichiometricratio for minimizing the hydrogen content.

[0044] One method of adjusting the stoichiometry of a capacitordielectric material is illustrated in FIG. 8. In this case, the ratio ofsilicon to nitrogen used in forming the silicon nitride is controlled,by controlling the relative proportions of silane, ammonia and nitrogengases that are used in a standard semiconductor silicon nitridedeposition process. The amount of the silicon in the silicon nitride isestablished by the silane. The amount of nitrogen is established bycontrolling the amounts of ammonia and nitrogen. By controlling therelative amounts of silane, ammonia and nitrogen, the desired silicon tonitrogen ratio is achieved. Of course, by controlling the silicon tonitrogen ratio to a relatively low value, a reduced amount of hydrogenis present in the silicon nitride. Silicon nitride with reduced amountof hydrogen content achieves the improvements and optimizations inelectrical and functional characteristics of the capacitor.

[0045] A similar method of controlling the ratio of silane, ammonia,nitrogen and oxygen to obtain a silicon oxynitride is shown in FIG. 9.Controlling the amounts of these four gases in order to obtain thedesired ratio of silicon to nitrogen in the resultant silicon oxynitrideis performed in the same manner as has been described in conjunctionwith FIG. 8, taking into account the difference in chemistry of siliconoxynitride compared to silicon nitride.

[0046] Another technique for obtaining the desired silicon to nitrogenratio in either silicon nitride or silicon oxynitride is to control thepower of the plasma enhanced chemical vapor deposition process forforming silicon nitride and silicon oxynitride dielectrics. The siliconnitride is formed by using plasma enhanced chemical vapor deposition(PECVD) in the conventional manner, except for controlling the power toobtain the desired amount of hydrogen in the formed capacitor dielectricmaterial. Silicon oxynitride is also formed in the conventional mannerusing PECVD, except for controlling the power to obtain the desiredhydrogen content in the formed capacitor dielectric material. Increasingthe low frequency power or a combination of both low and high frequencypowers used to deposit the film of silicon nitride or silicon oxynitrideincreases the induced DC bias, which is accompanied by an increase inionic bombardment. More extensive ionic bombardment causes adensification of the film as the film is deposited. The ionicbombardment breaks the bonds of hydrogen to the silicon and to thenitrogen and thus allows the hydrogen to separate from the silicon andnitrogen during the formation of the silicon nitride. A similarcircumstance exists with respect to breaking the bonds of the hydrogento silicon and to nitrogen during the formation of silicon oxynitride.Thus with greater power applied during plasma enhanced chemical vapordeposition, a greater number of hydrogen bonds are broken thus releasingthe hydrogen from the silicon nitride and silicon oxynitride.

[0047] In the case of silicon dioxide used as capacitor dielectricmaterial, an adjustment in the composition of the silicon dioxidematerial will result in substantially reducing the variance and valuesrepresented by the bars 38 of the graph 36, shown in FIG. 3. A techniquefor adjusting the composition of the silicon dioxide material to reducethe variance in values is illustrated in FIG. 11. In this technique, thesilicon dioxide is first formed using standard semiconductor fabricationtechnique for forming silicon dioxide. Thereafter the silicon dioxide issubjected to at least one and preferably a multiple number of thermalcycles using a nitrogen or reduced pressure environment. Each thermalcycle is accomplished by raising the temperature of the silicon oxide toapproximately 400 degrees Celsius, and then allowing it to cool to aconsiderably lesser temperature, for example approximately 150 degreesCelsius. With each thermal cycle, hydrogen bonds to the silicon arebroken, and some of the hydrogen contained within the silicon dioxide isfreed and replaced by nitrogen, thereby reducing the overall hydrogencontent of the silicon dioxide. The diminished hydrogen content of thesilicon dioxide causes less variability of its dC/dV characteristics, aswould be illustrated by smaller vertical bars 38, shown in FIG. 3.Reducing the range in the dC/dV characteristics makes the capacitor morepredictable in performance.

[0048] Reducing the hydrogen content of capacitor dielectric material,such as silicon nitride, silicon oxynitride or silicon dioxide, improvesor optimizes the electrical and functional characteristics of thecapacitor. Controlling or optimizing the stoichiometry of the capacitordielectric material effectively achieves control over the hydrogencontent. By keeping the silicon to nitrogen ratio low, about 1.0 orless, and preferably at approximately 0.75, the hydrogen content isoptimally diminished to achieve the best improvements in electrical andfunctional characteristics. In the case of silicon dioxide, repetitivethermal cycles break the hydrogen bonds and free the hydrogen from thecapacitor dielectric material to achieve a lower range in the dC/dVvalues for a silicon dioxide film. Controlling the low and highfrequency power associated with plasma enhanced chemical vapordeposition to achieve a predetermined level of breakage of the hydrogenbonds by higher energy ion bombardment also reduces the hydrogen contentand adjusts the composition of the capacitor dielectric material. Othertechniques for controlling the relative proportion of the components ofcapacitor dielectric material to reduce the hydrogen content, to controlthe number and breakage of hydrogen bonds in the material, and to adjustthe relative proportion of the components to indirectly control thehydrogen content of the capacitor dielectric material may be recognizedafter the improvements of the present invention have been understood.

[0049] Presently preferred embodiments of the invention and itsimprovements have been described with a degree of particularity. Thisdescription has been made by way of preferred example. It should beunderstood that the scope of the present invention is defined by thefollowing claims, and should not be unnecessarily limited by thedetailed description of the preferred embodiments set forth above.

The invention claimed is:
 1. A method of fabricating a capacitordielectric material in a capacitor, comprising the steps of: forming thecapacitor dielectric material to contain hydrogen; and adjusting acomposition of the capacitor dielectric material by controlling astoichiometry of the capacitor dielectric material in order to adjust anamount of the hydrogen contained in the capacitor dielectric materialand to obtain predetermined electrical or functional characteristics ofthe capacitor.
 2. A method as defined in claim 1 further comprising thesteps of: forming the capacitor dielectric material from substancesincluding silicon, nitrogen and hydrogen; and controlling astoichiometric ratio of silicon to nitrogen in the formed capacitordielectric material to limit the amount of hydrogen in the formedcapacitor dielectric material.
 3. A method as defined in claim 2 furthercomprising the step of: controlling the ratio of silicon to nitrogen toachieve a stoichiometric ratio of approximately 1.0 or less in theformed capacitor dielectric material.
 4. A method as defined in claim 3wherein the capacitor dielectric material is substantially siliconnitride.
 5. A method as defined in claim 3 wherein the capacitordielectric material is substantially silicon oxynitride.
 6. A method asdefined in claim 2 further comprising the step of: controlling the ratioof silicon to nitrogen to achieve a stoichiometric ratio ofapproximately 0.75 in the capacitor dielectric material.
 7. A method asdefined in claim 2 further comprising the steps of: forming thecapacitor dielectric material from substances also including oxygen;controlling the relative proportion of silicon, nitrogen, hydrogen andoxygen to obtain a stoichiometric ratio of silicon to nitrogen in theformed capacitor dielectric material of approximately 1.0 or less.
 8. Amethod as defined in claim 2 further comprising the steps of: usingsilane gas as the substance which includes silicon and hydrogen; usingammonia gas as the substance which includes nitrogen and hydrogen; usingnitrogen gas as the substance which includes nitrogen; using oxygen gasas an additional substance which includes oxygen; and controlling therelative proportions of the silane, ammonia and nitrogen gases whenforming the capacitor dielectric material to obtain a stoichiometricratio of silicon to nitrogen in the formed capacitor dielectric materialof approximately 1.0 or less.
 9. A method as defined in claim 1 furthercomprising the steps of: forming the capacitor dielectric material fromsubstances including silicon, nitrogen and hydrogen; forming thecapacitor dielectric material to include hydrogen bonds therein bydepositing the substances by using plasma enhanced chemical vapordeposition; breaking a predetermined number of the hydrogen bonds to thecapacitor dielectric material by ionic bombardment to allow the hydrogenfrom the broken bonds to escape from the capacitor dielectric material;controlling the power of the plasma enhanced chemical vapor depositionto establish the extent of the ion bombardment; and controlling theamount of the hydrogen remaining in the formed capacitor dielectricmaterial by controlling the power of the plasma enhanced chemical vapordeposition.
 10. A method as defined in claim 1 further comprising thesteps of: forming the capacitor dielectric material from substancesincluding silicon, nitrogen and hydrogen; forming the capacitordielectric material to have hydrogen bonds from the substances; breakinghydrogen bonds to the capacitor dielectric material by applying at leastone thermal cycle of temperature elevation and temperature reduction tothe capacitor dielectric material to allow the hydrogen from the brokenbonds to escape from the capacitor dielectric material; and controllingthe amount of the hydrogen in the formed capacitor dielectric materialby controlling the numbers and extent of thermal cycles applied to thecapacitor dielectric material.
 11. A method as defined in claim 10wherein the capacitor dielectric material is silicon dioxide.
 12. Acapacitor having plates and a dielectric material between the platesformed using the method of claim
 2. 13. A capacitor having plates and adielectric material between the plates formed using the method of claim9.
 14. A capacitor having plates and a dielectric material between theplates formed using the method of claim
 10. 15. A method of fabricatinga capacitor dielectric material, comprising the steps of: forming thecapacitor dielectric material from a first substance, a second substanceand a third substance, the formed capacitor dielectric material having acharacteristic that a stoichiometric ratio of the first and secondsubstances determines the amount of the third substance in the formedcapacitor dielectric material, the third substance having the capabilityto promote ionic conduction in the capacitor dielectric material; andcontrolling the stoichiometric ratio of the first and second substanceswhen forming the capacitor dielectric material to control the amount ofthe third substance in the formed capacitor dielectric material.
 16. Amethod as defined in claim 15 further comprising the step of:controlling the stoichiometric ratio of the first and second substancesto reduce the amount of the third substance in the capacitor dielectricmaterial to approximately its lowest practical amount.
 17. A method asdefined in claim 15 wherein the first, second and third substances aregases, and said method further comprises the step of: controlling therelative amounts of gas flow of the first and second substances whenforming the capacitor dielectric material to control the amount of thethird substance.
 18. A method as defined in claim 15 wherein the thirdsubstance is hydrogen.
 19. A method as defined in claim 18 wherein thecapacitor dielectric material is one of silicon nitride or siliconoxynitride.
 20. A capacitor having plates and a dielectric materialbetween the plates formed using the method of claim
 15. 21. A method offabricating a capacitor dielectric material, comprising the steps of:forming the capacitor dielectric material from substances including onesubstance having the capability to promote ionic conduction in thecapacitor dielectric material; depositing the substances by plasmaenhanced chemical vapor deposition to form the capacitor dielectricmaterial; breaking bonds of the one substance to the capacitordielectric material by ionic bombardment during the plasma enhancedchemical vapor deposition to allow the first substance from the brokenbonds to escape the capacitor dielectric material; and controlling theamount of the one substance in the formed capacitor dielectric materialby controlling the power of the plasma enhanced chemical vapordeposition to control the extent of breaking of the bonds of the onesubstance.
 22. A method as defined in claim 21 wherein the one substanceis hydrogen.
 23. A method as defined in claim 22 wherein the capacitordielectric material is one of silicon nitride or silicon oxynitride. 24.A capacitor having plates and a dielectric material between the platesformed using the method of claim
 21. 25. A method of fabricating acapacitor dielectric material, comprising the steps of: forming thecapacitor dielectric material from substances including one substancehaving the capability to promote ionic conduction in the capacitordielectric material; breaking bonds of the one substance to thecapacitor dielectric material by applying at least one thermal cycle oftemperature elevation and temperature reduction of the capacitordielectric material; and controlling the amount of the one substance inthe formed capacitor dielectric material by controlling the number andextent of the applications of thermal cycles to the capacitor dielectricmaterial.
 26. A method as defined in claim 25 wherein the one substanceis hydrogen.
 27. A method as defined in claim 26 wherein the capacitordielectric material comprises silicon dioxide.
 28. A capacitor havingplates and a dielectric material between the plates formed using themethod of claim
 25. 29. A capacitor having plates and a dielectricmaterial comprising silicon, nitrogen and hydrogen formed between theplates, the dielectric material having a stoichiometric ratio of siliconto nitrogen of approximately 1.0 or less.
 30. A capacitor as defined inclaim 29 wherein the stoichiometric ratio is approximately 0.75.